In these experiments the effect of aging and hypertension on regional hemodynamics is being investigated with the use of radioactive microspheres. Young and aged spontaneously hypertensive (SH) and Wistar Kyoto (WK) rats (3-24 months) are being tested in an unanesthetized state and during anesthesia with several clinically related anesthetic agents, including halothane, barbiturates and nitrous oxide with morphine agonists. We are evaluating the effect that chronic hypertension has on regional blood flow distribution in the rat and how changes in regional vascular tone and/or structural changes may affect autoregulation and the ability of the animal to compensate for blood loss and hypotension, maintaining perfusion of vital organs. A special emphasis will be maintained in these experiments on the cerebrovascular system. Aged chronic hypertensive SH will be compared to aged normotensive WK and also young rats for changes which may occur in cerebral blood flow (CBF), cerebral metabolic rate (CMR O2) and autoregulation. Anesthetic agents indicated above will be administered to aged and young rats to test their effect on CBF and CMR O2. Additional experiments are planned using antihypertensive therapy to lower blood pressure of young and aged SH and to compare autoregulation of regional beds and brain compared to untreated hypertensives.